Alright, I found a solution myself as a suggestion at the end of the
following page:
http://exchange.nagios.org/directory/Plugins/Others/Check_Svn/details
and that was to use the && concatenator instead of a semicolon. Since
"export" command cannot fail under normal circumstances, the behavior
devolves into being identical to semicolon, but nagios command
interpreter won't strip it.
export HOME=/var/lib/nagios && rest of sendmail command
Thanks guys, happy hearts n hooves. :P
- - Jesse Thompson